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MIC5020
Micrel, Inc.
MIC5020
Current-Sensing Low-Side MOSFET Driver
General Description
The MIC5020 low-side MOSFET driver is designed to operate at frequencies greater than 100kHz (5kHz PWM for 2% to 100% duty cycle) and is an ideal choice for high-speed applications such as motor control, SMPS (switch mode power supplies), and applications using IGBTs. The MIC5020 can also operate as a circuit breaker with or without automatic retry. The MIC5020's maximum supply voltage lends itself to control applications using up to 50V. The MIC5020 can control MOSFETs that switch voltages greater than 50V. A rising or falling edge on the input results in a current source or sink pulse on the gate output. This output current pulse can turn on or off a 2000pF MOSFET in approximately 175ns. The MIC5020 then supplies a limited current (< 2mA), if necessary, to maintain the output state. An overcurrent comparator with a trip voltage of 50mV makes the MIC5020 ideal for use with a current sensing MOSFET. An external low value resistor may be used instead of a sensing MOSFET for more precise overcurrent control. An optional external capacitor connected to the CT pin may be used to control the current shutdown duty cycle from 20% to < 1%. A duty cycle from 20% to about 75% is possible with an optional pull-up resistor from CT to VDD. An open collector output provides a fault indication when the sense inputs are tripped. The MIC5020 is available in 8-pin SOIC package. Other members of the MIC502x series include the MIC5021 high-side driver and the MIC5022 half-bridge driver with a cross-conduction interlock.
Features
* * * * * * * * * * * * * 11V to 50V operation 175ns rise/fall time driving 2000pF TTL compatible input with internal pull-down resistor Overcurrent limit Fault output indication Gate to source protection Compatible with current sensing MOSFETs Lamp control Heater control Motor control Solenoid switching Switch-mode power supplies Circuit breaker
Applications
Ordering Information
Part Number Standard MIC5020BM Pb-Free MIC5020YM Temperature Range -40C to +85C Package 8-pin SOIC
Typical Application
V+
+11V to +50V 10F 150kHz max.
1 2 3
MIC5020
V DD Input Fault CT Gate SenseSense+ Gnd
8 7 6 5
N-Channel Power MOSFET R S E N S E = 50mV I TR IP
optional*
4
R SENSE
* increases time before retry
Low-Side Driver with Overcurrent Trip and Retry
Micrel, Inc. * 2180 Fortune Drive * San Jose, CA 95131 * USA * tel + 1 (408) 944-0800 * fax + 1 (408) 474-1000 * http://www.micrel.com
July 2005
1
MIC5020
MIC5020
Micrel, Inc.
Pin Configuration
1 2 3 4
V DD
Gate 8
Input Sense- 7
Fault Sense+ 6
CT
Gnd 5
SOIC Package (M)
Block Diagram
6V Internal Regulator I1 CINT 2I1
Fault Normal
CT
Fault
Q1
Sense+ Sense50mV
ONE SHOT
ON OFF
VDD
6V
Input
10I2
I2
Gate
Transistor Count: 82
Pin Description
Pin Number 1 2 3 Pin Name Input Fault VDD Pin Function Supply: +11V to +50V. Decouple with 10F capacitor. TTL Compatible Input: Logic high turns the external MOSFET on. An internal pull-down returns an open pin to logic low. Overcurrent Fault Indicator: When the sense voltage exceeds threshold, open collector output is open circuit for 5s (tG(ON)), then pulled low for tG(OFF). tG(OFF) is adjustable from CT. Retry Timing Capacitor: Controls the off time (tG(OFF)) of the overcurrent retry cycle. (Duty cycle adjustment.) * Open = 20% duty cycle. * Capacitor to Ground = approx. 20% to <1% duty cycle. * Pull-Up resistor = approx. 20% to approx. 75% duty cycle. * Ground = maintained shutdown upon overcurrent condition.
4
CT
5 6
Gnd Sense +
Circuit Ground Current Sense Comparator (+) Input: Connect to high side of sense resistor or current sensing MOSFET sense lead. A built-in offset in conjunction with RSENSE sets the load overcurrent trip point. Current Sense Comparator (-) Input: Connect to the low side of the sense resistor (usually power ground).
7 8
Sense - Gate
Gate Drive: Drives the gate of an external power MOSFET. Also limits VGS to 15V max. to prevent Gate to Source damage. Will sink and source current.
MIC5020
2
July 2005
MIC5020
Micrel, Inc.
Absolute Maximum Ratings
Supply Voltage (VDD)................................................... +55V Input Voltage .................................................-0.5V to +15V Sense Differential Voltage .......................................... 6.5V Sense + or Sense - to Gnd ...........................-0.5V to +50V Fault Voltage ............................................................... +50V Current into Fault ........................................................ 50mA Timer Voltage (CT) ...................................................... +5.5V
Operating Ratings
Supply Voltage (VDD)......................................+11V to +50V Temperature Range SOIC ....................................................... -40C to +85C
Electrical Characteristics
Symbol Parameter D.C. Supply Current
TA = 25C, Gnd = 0V, VDD = 12V, Sense +,- = 0V, Fault = Open, CT = Open, Gate CL = 1500pF unless otherwise specificed Condition VDD = 12V, Input = 0V VDD = 50V, Input = 0V VDD = 12V, Input = 5V Input Threshold Input Hysteresis Input Pull-Down Current Fault Output Saturation Voltage Fault Output Leakage Current Limit Threshold Gate On Voltage tG(ON) tDLH tR tF tDLH fmax
Note 1 Note 2 Note 3 Note 4 Note 5 Note 6 Note 7
Min
Typ 0.8 2 0.8 4
Max 2 10 2 25 2.0 40 0.4 +1 70 18 10 50 800 1500 1500 1500
Units mA mA mA mA V V A V A mV V V s s ns ns ns ns kHz
VDD = 50V, Input = 5V
0.8 10
1.4 0.1 20 0.15
Input = 5V Fault Current = 1.6mA Note 1 Fault = 50V Note 2 VDD = 50V VDD = 12V Sense Differential > 70mV
-1 30 10 14 2 10
0.01 50 11 15 5 20 400 700 900 500
Gate On Time, Fixed Gate Off Time, Adjustable Gate Turn-On Delay Gate Rise Time Gate Turn-Off Delay Gate Fall Time Maximum Operating Frequency
Voltage remains low for time affected by CT.
tG(OFF)
Sense Differential > 70mV, CT = 0pF Note 3 Note 4 Note 5 Note 6 Note 7
100
150
When using sense MOSFETs, it is recommended that RSENSE < 50. Higher values may affect the sense MOSFET's current transfer ratio. Input switched from 0.8V (TTL low) to 2.0V (TTL high), time for Gate transition from 0V to 2V. Input switched from 0.8V (TTL low) to 2.0V (TTL high), time for Gate transition from 2V to 10V. Input switched from 2.0V (TTL high) to 0.8V (TTL low), time for Gate transition from 11V (Gate ON voltage) to 10V. Input switched from 2.0V (TTL high) to 0.8V (TTL low), time for Gate transition from 10V from 2V. Frequency where gate on voltage reduces to 10V with 50% input duty cycle.
July 2005
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MIC5020
MIC5020
Micrel, Inc.
Typical Characteristics
Supply Current vs. Supply Voltage
VIN = 5V
3.5 3.0
ISUPPLY (mA)
900 800
tON (nS)
Turn-On Time vs. Supply Voltage
VG AT E = 4V CL = 1500pF VIN = 0 to 5V Sq. Wave
1200 1100
tOFF (ns)
Turn-Off Time vs. Supply Voltage
2.5 2.0 1.5 1.0 0.5
700 600 500
INCLUDES PROPAGATION DELAY
1000 900 800
VG AT E = 4V CL = 1500pF VIN = 0 to 5V Sq. Wave
INCLUDES PROPAGATION DALAY
VIN = 0V
5 10 15 20 25 30 35 40 45 50 VSUPPLY (V)
400
700
5 10 15 20 25 30 35 40 45 50 VSUPPLY (V)
5
10
15 20 VSUPPLY (V)
25
30
100 80
IIN (A)
Input Current vs. Input Voltage
VSUPPLY = 12V
1200 1000
Turn-On Time vs. Gate Capacitance
VG AT E = 4V
25.0
Shutdown Duty Cycle (%)
Overcurrent Shutdown Retry Duty Cycle
tON = 5s VSUPPLY = 12V
20.0 15.0 10.0 5.0 0.0 0.1
tON (ns)
60 40 20 0
800 600 400
INCLUDES PROPAGATION DELAY
0
5
10 15 VIN (V)
20
25
200 1x102
1x103 1x104 CGATE (pF)
1x105
1
10 100 CT (pF)
1000 10000
80 70 VOLTAGE (mV) 60 50 40 30
Sense Threshold vs. Temperature
Input Gate
TTL (H) 0V
15V (max.)
Sense +, - Differential Fault
0V 50mV
0V Off On
20 -60 -30 0 30 60 90 120 150 TEMPERATURE (C)
Timing Diagram 1. Normal Operation
5s
20s
Input Gate
TTL (H) 0V
15V (max.)
5s
Input Gate
TTL (H) 0V
15V (max.)
Sense +,- Differential Fault
0V 50mV
0V Off On
Sense +,- Differential Fault
0V 50mV
0V Off On
Timing Diagram 2. Fault Condition, CT = Open MIC5020 4
Timing Diagram 3. Fault Condition, CT = Grounded July 2005
MIC5020
Micrel, Inc. MOSFET Q1. A fault condition (> 50mV from SENSE + to SENSE -) causes the overcurrent comparator to enable current sink 2I1 which overcomes current source I1 to discharge CINT in a short time. When CINT is discharged, the INPUT is disabled, which turns off the GATE output; the FAULT output is enabled; and CINT and CT are ready to be charged. When the GATE output turns the MOSFET off, the overcurrent signal is removed from the sense inputs which deactivates current sink 2I1. This allows CINT and the optional capacitor connected to CT to recharge. A Schmitt trigger delays the retry while the capacitor(s) recharge. Retry delay is increased by connecting a capacitor to CT (optional). The retry cycle will continue until the the fault is removed or the input is changed to TTL low. If CT is connected to ground, the circuit will not retry upon a fault condition. Fault Output The FAULT output is an open collector transistor. FAULT is active at approximately the same time the output is disabled by a fault condition (5s after an overcurrent condition is sensed). The FAULT output is open circuit (off) during each successive retry (5s).
Functional Description
Refer to the MIC5020 block diagram. Input A signal greater than 1.4V (nominal) applied to the MIC5020 INPUT causes gate enhancement on an external MOSFET turning the external MOSFET on. An internal pull-down resistor insures that an open INPUT remains low, keeping the external MOSFET turned off. Gate Output Rapid rise and fall times on the GATE output are possible because each input state change triggers a one-shot which activates a high-value current sink (10I2) for a short time. This draws a high current through a current mirror circuit causing the output transistors to quickly charge or discharge the external MOSFET's gate. A second current sink continuously draws the lower value of current used to maintain the gate voltage for the selected state. An internal 15V Zener diode protects the external MOSFET by limiting the gate output voltage when VDD is connected to higher voltages. Overcurrent Limiting Current source I1 charges CINT upon power up. An optional external capacitor connected to CT is discharged through
Applications Information
The MIC5020 MOSFET driver is intended for low-side switching applications where higher supply voltage, overcurrent sensing, and moderate speed are required. Supply Voltage A feature of the MIC5020 is that its supply voltage rating of up to 50V is higher than many other low-side drivers. The minimum supply voltage required to fully enhance an N-channel MOSFET is 11V. A lower supply voltage may be used with logic level MOSFETs. Approximately 6V is needed to provide 5V of gate enhancement. Low-Side Switch Circuit Advantages A moderate-speed low-side driver is generally much faster than a comparable high-side driver. The MIC5020 can provide the gate drive switching times and low propagation delay times that are necessary for high-frequency high-efficiency circuit operation in PWM (pulse width modulation) designs used for motor control, SMPS (switch mode power supply) and heating element control. Switched loads (on/off) can benefit from the MIC5020's fast switching times by allowing use of MOSFETs with smaller safe operating areas. (Larger MOSFETs are often required when using slower drivers.) Overcurrent Limiting A 50mV comparator is provided for current sensing. The low level trip point minimizes I2R losses when power resistors are used for current sensing. Flexibility in choosing drain or source side sensing is provided by access to both SENSE + and SENSE - comparator inputs. The adjustable retry feature can be used to handle loads with high initial currents, such as lamps, motors, or heating elements and can be adjusted from the CT connection. CT to ground causes maintained gate drive shutdown following overcurrent detection. CT open, or through a capacitor to ground, causes automatic retry . The default duty cycle (CT open) is approximately 20%. Refer to the electrical characteristics when selecting a capacitor for a reduced duty cycle. CT through a pull-up resistor to VDD increases the duty cycle. Increasing the duty cycle increases the power dissipation in the load and MOSFET. Circuits may become unstable at a duty cycles of about 75% or higher, depending on the conditions. Caution: The MIC5020 may be damaged if the voltage on CT exceeds the absolute maximum rating. An overcurrent condition is externally signaled by an open collector (FAULT) output. The MIC5020 may be used without current sensing by connecting SENSE + and SENSE - to ground. Current Sense Resistors Lead length can be significant when using low value (< 1) resistors for current sensing. Errors caused by lead length can be avoided by using four-terminal current sensing resistors. Four-terminal resistors are available from several manufacturers.
July 2005
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MIC5020
MIC5020 Lamp Driver Application Incandescent lamps have a high inrush current (low resistance) when turned on. The MIC5020 can perform a "soft start" by pulsing the MOSFET (overcurrent condition) until the filament is warm enough for its current to decrease (resistance increases). The sense resistor is selected so the voltage across the sense resistor drops below the sense threshold (50mV) as the filament becomes warm. The MOSFET is no longer pulsed to limit current and the lamp turns completely on.
V+
Micrel, Inc. Current Sensing MOSFET Application A current sensing MOSFET allows current sensing without adding additional resistance to the power switching circuit. A current sensing MOSFET has two source connections: a "power source" for power switching and a "current source" for current sensing. The current from the current source is approximately proportional to the current through the power source, but much smaller. A current sensing ratio (ISOURCE/ ISENSE) is provided by the MOSFET manufacturer.
V+ (+13.2V, > 4.4A)
(3, > 60W)
(+11V to +12V)
Incandescent Lamp (#1157)
+11V to +50V (+13.2V) 10F
10F
TTL Input (0V/5V)
1 2 3 4
MIC5020
V DD Input Fault CT
Gate SenseSense+ Gnd
8 7 6 5
N-Channel Power MOSFET (IRF540)
1 2 3 4
MIC5020
V DD Input Fault CT
Gate SenseSense+ Gnd
8 7 6 5
TTL Input (0V/5V)
N-Channel Current Sensing Power MOSFET (IRCZ24)
R SENSE (10)
RS E N S E (0.041)
"( )" values apply to demo circuit. See text.
"( )" values apply to demo circuit. See text.
Figure 1. Lamp Driver with Current Sensing A lamp may not fully turn on if the filament does not heat up adequately. Changing the duty cycle, sense resistor, or both to match the filament characteristics can correct the problem. Soft start can be demonstrated using a #1157 dual-filament automotive lamp. The value of RS shown in figure 1 allows for soft start of the higher-resistance filament (measures approx. 2.1 cold or 21 hot). Solenoid Driver Application The MIC5020 can be directly powered by the control voltage supply in typical 11Vdc through 50Vdc control applications. Current sensing has been omitted as an example.
V+
Figure 3. Using a Current Sensing MOSFET The MOSFET current source is used to develop a voltage across a sense resistor. This voltage is monitored by the MIC5020 (SENSE + and SENSE - pins) to identify an overcurrent condition. The value of the sense resistor can be estimated with: RSENSE = (r VTRIP RDS(ON)) / (ILOAD RDS(ON) - VTRIP) where: RSENSE = external "sense" resistor VTRIP = 50mV (0.050V) for the MIC5020 r = manufacturer's current sense ratio: (ISOURCE/ISENSE) RDS(ON) = manufacturer's power source on resistance ILOAD = load current (power source current) The drain to source voltage under different fault conditions affects the behavior of the MOSFET current source; that is, the current source will respond differently to a slight over-current condition (VDS(ON) very small) than to a short circuit (where VDS(ON) is approximately equal to the supply voltage). Adjustment of the sense resistor value by experiment starting from the above formula will provide the quickest selection of RSENSE. Refer to manufacture's data sheets and application notes for detailed information on current sensing MOSFET characteristics. Figure 3 includes values which can be used to demonstrate circuit operation. The IRCZ24 MOSFET has a typical sense ratio of 780 and a RDS(ON) of 0.10. A large 3 wirewound load resistor will cause inductive spikes which should be suppressed using a diode (using the same configuration as figure 2).
+11V to +50V
MIC5020
V DD Input Fault CT
Solenoid
Diode
10F
TTL Input
1 2 3 4
Gate SenseSense+ Gnd
8 7 6 5
N-Channel Power MOSFET
Figure 2. Solenoid Driver, Without Current Sensing A diode across the load protects the MOSFET from the voltage spike generated by the inductive load upon MOSFET turn off. The peak forward current rating of the diode should be greater than the load current.
MIC5020
6
July 2005
MIC5020 Faster MOSFET Switching The MIC5020's GATE current can be multiplied using a pair of bipolar transistors to permit faster charging and discharging of the external MOSFET's gate.
+40V max.
Micrel, Inc. For test purposes, a 680 load resistor and 3 sense resistor will produce an overcurrent condition when the load's supply (V+) is approximately 12V or greater. Low-Temperature Operation As the temperature of the MIC5020AJB (extended temperature range version--no longer available) approaches -55C, the driver's off-state, gate-output offset from ground increases. If the operating environment of the MIC5020AJB includes low temperatures (-40C to -55C), add an external 2.2M resistor as shown in Figures 6a or 6b. This assures that the driver's gate-to-source voltage is far below the external MOSFET's gate threshold voltage, forcing the MOSFET fully off.
V+
+11V to +50V 10F
150kHz max.
1 2 3 4
MIC5020
V DD Input Fault CT
2N3904
8 7 6 5
N-Channel Power MOSFET (IRF540)
Gate SenseSense+ Gnd
2N3906
+11V to +50V
1 2 3 4
MIC5020
V DD Input Fault CT
Gate SenseSense+ Gnd
8 7 6 5
2.2M
Figure 4. Faster MOSFET Switching Circuit NPN and PNP transistors are used to respectively charge and discharge the MOSFET gate. The MIC5020 gate current is multiplied by the transistor . The switched circuit voltage can be increased above 40V by selecting transistors with higher ratings. Remote Overcurrent Limiting Reset In circuit breaker applications where the MIC5020 maintains an off condition after an overcurrent condition is sensed, the CT pin can be used to reset the MIC5020.
V+
10F
RS E NS E
Figure 6a. Gate-to-Source Pull Down The gate-to-source configuration (refer to Figure 6a) is appropriate for resistive and inductive loads. This also causes the smallest decrease in gate output voltage.
V+
+11V to +50V 10F
1 2 3
MIC5020
V DD Input Fault CT
Gate SenseSense+ Gnd
8 7 6 5
+11V to +50V
N-Channel Power MOSFET
1 2 3 4
MIC5020
V DD Input Fault CT
Gate SenseSense+ Gnd
8 7 6 5
2.2M RS E N S E
10F
TTL input
Retry (H) Maintained (L)
10k to 100k
4
74HC04 (example)
Q1 2N3904
RS E N S E
Figure 6b. Gate-to-Ground Pull Down The gate-to-ground configuration (refer to Figure 6b) is appropriate for resistive, inductive, or capacitive loads. This configuration will decrease the gate output voltage slightly more than the circuit shown in Figure 6a.
Figure 5. Remote Control Circuit Switching Q1 on pulls CT low which keeps the MIC5020 GATE output off when an overcurrent is sensed. Switching Q1 off causes CT to appear open. The MIC5020 retries in about 20s and continues to retry until the overcurrent condition is removed.
July 2005
7
MIC5020
MIC5020
Micrel, Inc.
Package Information
0.026 (0.65) MAX) PIN 1
0.157 (3.99) 0.150 (3.81)
DIMENSIONS: INCHES (MM)
0.050 (1.27) TYP
0.020 (0.51) 0.013 (0.33) 0.0098 (0.249) 0.0040 (0.102) 0-8 SEATING PLANE 45 0.010 (0.25) 0.007 (0.18)
0.064 (1.63) 0.045 (1.14)
0.197 (5.0) 0.189 (4.8)
0.050 (1.27) 0.016 (0.40) 0.244 (6.20) 0.228 (5.79)
8-Pin SOIC (M)
MICREL INC.
TEL + 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB http://www.micrel.com
2180 FORTUNE DRIVE
SAN JOSE, CA 95131
USA
This information furnished by Micrel in this data sheet is believed to be accurate and reliable. However no responsibility is assumed by Micrel for its use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer. Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser's use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser's own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. (c) 1998 Micrel, Inc.
MIC5020
8
July 2005

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